The invention relates to a method and to an apparatus for treating water which contains dissolved salt to produce water which is substantially or totally free from salt, employing the operations of partial evaporation of the saline feed water and condensation of the resulting vapor, the unvaporized fraction of the water being enriched in salt and discharged from the system. The invention is principally, but not exclusively, applicable to the treatment of sea water to produce water suitable for agricultural uses and which may be or can be made potable.
A major difficulty with known desalting plants which use the principle of vaporization has been the deposition of scale on the surfaces of the equipment, especially heat exchangers and vaporizers, but affecting also other parts that come into contact with brine. These surfaces are usually inaccessible and, therefore, difficult to clean. The deposition of scale is especially severe when brine is in contact with heated walls, and the severity of the problem increases as the concentration of the salt in the refuse water and the temperature are increased.
Prior art attempts to eliminate these shortcomings have not been too successful and, furthermore, were economically unfeasible. For example, U.S. Pat. No. 2,921,004 suggests to initially heat water in a flame, then transfer it to a vacuumized flash chamber to evaporate part of the water. This process is cumbersome and relatively inefficient. U.S. Pat. No. 3,026,261 suggests an approach in which an aqueous slurry of finely divided solids is mixed with the saline water. The mixture is then heated above its labile supersaturation point so that the dissolved salt precipitates on the solids. Difficult material handling problems make this approach commercially unfeasible.